The long-term goal of this project is to understand the neural mechanisms underlying restored hearing by cochlear implants (CI). We propose a new non-human primate model for CI research, the common marmoset (Callithrix jacchus). Marmosets have a rich vocal repertoire, are highly communicative, and can potentially be used to study vocal production and auditory feedback mechanisms related to speech processing in CI subjects. Its hearing range is similar to that of humans and its auditory cortex shares similar organizations as humans, making it a valuable model to address issues in CI research pertaining to human users. As a first step towards our long term goal, we will examine the basic response properties of neurons in marmoset AC to electrical stimulation of the cochlea using both acute and chronic recording techniques. Aim 1 is to map activation areas in AC elicited by acoustic tone and electric current pulse stimuli. First, neural activity will be recorded from many sites across the tonotopic axis of primary AC in response to acoustic stimuli. The animal will then be deafened and implanted with a multi-channel CI electrode, and similar mapping will be conducted in response to electric stimulation. Activity patterns across AC in response to acoustic and electric stimuli will be compared, and the specificity and cochlear frequency-place areas of stimulation will be assessed. To allow for complete mapping in a short amount of time, this study will be done acutely in anesthetized marmosets. Because no one has ever attempted CI in marmosets, the experiments proposed in Aim 1 are necessary for us to establish this new CI model. Clinical CI processors use modulated pulse trains to transmit temporal features important in speech, so it is of great interest how such signals are represented in the brain. Since anesthesia influences temporal processing of cortical neurons, Aim 2 is to study the neural representation of temporally modulated electric pulse trains in awake, chronically implanted marmosets. The results of these aims will help elucidate brain processes involved in electric hearing, and establish the marmoset as a viable model for future CI research. The research and training goals in this grant define a year-by-year plan for the applicant that help prepare him to become an independent and successful academic researcher. The methods and procedures he will learn will allow him to (a) perform and critically analyze auditory research, (b) disseminate knowledge through written publications, (c) orally communicate research findings, (d) organize research goals through grant writing, and (e) conduct proper research practices through continued ethics training. To complete these objectives, the pre-doctoral student will be closely mentored by two sponsors in the Dept of Biomedical Engineering and Otolaryngology - Head & Neck Surgery. A detailed plan for training and mentorship is presented.